Properly setup, and assuming they're in good condition, a 1.5 is fine for fox. But, keep in mind, it may not hold the occassional coyote or bobcat. It may, but it also may not. Make sure the chain isn't terribly long so they can't get a running start to jolt out of the trap, well swiveled, staked well, and a shock spring probably wouldn't hurt either.

I honestly don't know about the whole myth of canines being detered by the scent of steel. When you consider that many traps don't have their chain waxed and still catch plenty of fur, I think it's more a myth than anything. Besides, one of foxes' favorite hunting grounds is around rusted farm equipment because that's where the mice hang out.